A mobile handset has to be designed to accommodate multi-path signals that may be present in the received signal, and for this purpose it incorporates a multi-path searcher which identifies the strongest of the multi-path signals to use. In a W-CDMA system, the Common Pilot Channel (CPICH) contains a predetermined sequence of pilot bits spread with known channelisation codes and scrambled with known scrambling codes, and the multi-path searcher makes measurements on the CPICH signal by correlating this against the known CPICH scrambled chip sequence to identify the path positions and select a sub-set to use for decoding. The multi-path searcher consists of multiple correlators which each process the same scrambling sequence and channelisation code to carry out a correlation measurement on the received signal after it has been delayed by a different time delay at the input of each correlator, the multiple correlation measurements so generated being analysed in relation to the time delays to identify the multi-path positions. In order to improve the accuracy and reliability in detecting path positions, the correlation process is extended over an integration time sufficient to identify the path positions above the noise floor of the signal. However, an increase in integration time results in an increase in processor/ASIC size and power consumption, which in turn leads to an increase in the manufacturing cost of the handset
In addition, there is a requirement in the W-CDMA standard that a handset should be able to handle multi-path signals, as described above, in connection with multi-path CPICH signals corresponding to different cells of the cellular network, and that multi-path measurements should be made in relation to a predetermined number of cells should within a predetermined time, each cell being identified by its own scrambling code and channelisation code. Thus, if a multi-path searcher is used to make successive multi-path measurements in relation to multiple cells, the integration time for each is limited. Alternatively, if multiple multi-path searchers are provided to handle the multiple cells in parallel, then the manufacturing cost and power consumption is increased.
An object of the invention is to provide multi-path searching in such a manner as to mitigate the above problems.